ACS BIOCHEMISTRY MOLECULAR
SCIENCE REVIEW 2026 QUESTIONS
WITH SOLUTIONS TESTED QUESTIONS.
▶ Calculation for pH and pKa. Answer: pH= -log[H3O+]
pKa= -log(Ka)
▶ Normal blood pH range. Answer: 7.35-7.45
▶ The Hydrophobic Effect. Answer: When non-polar molecules
aggregate in the presence of water, minimizing the entropy decrease
water must go through to order themselves around the border of the non-
polar molecule. Reducing the surface area water must organize around
increases entropy, which is favorable.
The aggregation is responsible for the formation of a variety of lipid
structures in the body, including cell membranes.
▶ Buffers. Answer: Composed of a weak acid (HA) and its conjugate
base (A-). Added acid reacts with A-, and added base reacts with HA,
giving a limited overall pH change.
,Two main reactions:
1) When excess base is added:
OH-+HA-->H2O+A-
2) When excess acid is added:
H+ + A- -->HA
**So, the net result is more of the weak acid and its conjugate base**
▶ When are buffers optimal? What equation can we use for this?.
Answer: When [HA]= [A-], occurring when pH=pKa
Henderson- Hasselbalch allows use to calculate pH at given pKa, and
vice versa:
▶ Blood Buffering. Answer: Components:
1) carbonic acid (H2CO3) (weak acid). pKa= 6.1.
2) Bicarbonate Ion (HCO3-), conjugate base of carbonic acid
3) H+ (hydrogen ion)
If OH- (base) is added, Carbonic acid buffers it into bicarbonate ion and
water.
If H+ (acid) is added, bicarbonate ions and H+ buffer it to carbonic acid.
,▶ Amino Acids, peptides, and polypeptides. Answer: the building blocks
of proteins, a chain of which is called a peptide. There are 20 standard
amino acids that act as the monomers to make protein polymers!
A long peptide is called a polypeptide!
Proteins are composed of one or more polypeptide chain.
▶ Peptide bonds. Answer: Between the C and N of C=O and N-H of two
adjacent amino acids.
▶ What wavelength is indicative of aromatic amino acids?. Answer: 280
nm, with tryptophan absorbing more, tyrosine absorbing a bit less, and
phenylalanine absorbing a lot less.
▶ Stereochemistry of amino acids. Answer: Every carbon except for
glycine is a chiral center, giving two possible structures for each: L and
D (except for glycine).
L is the only one found in nature.
, ▶ Acid-Base properties of amino acids. Answer: Each has at least two
ionizable protons (from the COOH and NH3 groups), but most have
others.
COOH pKa: 2.34
NH3 pKa: 29.60
▶ PI. Answer: the isoelectric point, or the pH at which an amino acid or
peptide has no net charge.
- At pH= PI, the predominant species is the zwitterion
- At pH<PI, the predominant species is net positive
- At pH>PI, the predominant species is net negative
**At PI, amino acid or peptide cannot migrate through an electric field,
so this is a way we can separate amino acids (by PI via electric field!)**
▶ How to calculate PI, or isoelectric pint. Answer: Average pKa values
involving the neutral species
For glycine, that only has COOH and NH3 pKa's, the PI is the average
between 2.34 and 9.60, so 5.97!
SCIENCE REVIEW 2026 QUESTIONS
WITH SOLUTIONS TESTED QUESTIONS.
▶ Calculation for pH and pKa. Answer: pH= -log[H3O+]
pKa= -log(Ka)
▶ Normal blood pH range. Answer: 7.35-7.45
▶ The Hydrophobic Effect. Answer: When non-polar molecules
aggregate in the presence of water, minimizing the entropy decrease
water must go through to order themselves around the border of the non-
polar molecule. Reducing the surface area water must organize around
increases entropy, which is favorable.
The aggregation is responsible for the formation of a variety of lipid
structures in the body, including cell membranes.
▶ Buffers. Answer: Composed of a weak acid (HA) and its conjugate
base (A-). Added acid reacts with A-, and added base reacts with HA,
giving a limited overall pH change.
,Two main reactions:
1) When excess base is added:
OH-+HA-->H2O+A-
2) When excess acid is added:
H+ + A- -->HA
**So, the net result is more of the weak acid and its conjugate base**
▶ When are buffers optimal? What equation can we use for this?.
Answer: When [HA]= [A-], occurring when pH=pKa
Henderson- Hasselbalch allows use to calculate pH at given pKa, and
vice versa:
▶ Blood Buffering. Answer: Components:
1) carbonic acid (H2CO3) (weak acid). pKa= 6.1.
2) Bicarbonate Ion (HCO3-), conjugate base of carbonic acid
3) H+ (hydrogen ion)
If OH- (base) is added, Carbonic acid buffers it into bicarbonate ion and
water.
If H+ (acid) is added, bicarbonate ions and H+ buffer it to carbonic acid.
,▶ Amino Acids, peptides, and polypeptides. Answer: the building blocks
of proteins, a chain of which is called a peptide. There are 20 standard
amino acids that act as the monomers to make protein polymers!
A long peptide is called a polypeptide!
Proteins are composed of one or more polypeptide chain.
▶ Peptide bonds. Answer: Between the C and N of C=O and N-H of two
adjacent amino acids.
▶ What wavelength is indicative of aromatic amino acids?. Answer: 280
nm, with tryptophan absorbing more, tyrosine absorbing a bit less, and
phenylalanine absorbing a lot less.
▶ Stereochemistry of amino acids. Answer: Every carbon except for
glycine is a chiral center, giving two possible structures for each: L and
D (except for glycine).
L is the only one found in nature.
, ▶ Acid-Base properties of amino acids. Answer: Each has at least two
ionizable protons (from the COOH and NH3 groups), but most have
others.
COOH pKa: 2.34
NH3 pKa: 29.60
▶ PI. Answer: the isoelectric point, or the pH at which an amino acid or
peptide has no net charge.
- At pH= PI, the predominant species is the zwitterion
- At pH<PI, the predominant species is net positive
- At pH>PI, the predominant species is net negative
**At PI, amino acid or peptide cannot migrate through an electric field,
so this is a way we can separate amino acids (by PI via electric field!)**
▶ How to calculate PI, or isoelectric pint. Answer: Average pKa values
involving the neutral species
For glycine, that only has COOH and NH3 pKa's, the PI is the average
between 2.34 and 9.60, so 5.97!
